Not applicable.
This invention is in the field if wireless telephony, and is more directed to the control of power amplifiers in wireless telephone handsets.
Modern advanced mobile computing devices and wireless telephone handsets are evolving from the so-called second generation (2G) technologies for wireless communications toward the capability of providing the so-called third generation (3G) wireless services. These 3G services are expected to extend current second generation voice and data services, by including new very high bandwidth entertainment services such as video and CD quality audio, interactive messaging including video and graphics, videoconferencing, video streaming, and remote control and monitoring services.
Examples of 2G communications standards include Global System for Mobile (GSM). Extensions of these approaches that are evolving toward 3G services include Enhanced Data rates for GSM Evolution (EDGE), which involves an eight-level phase shift keying (8-PSK) modulation of a 200 kHz carrier, and CDMA 2000, which is an evolution from the TIA IS-95 code division multiple access (CDMA) standard. 3G cellular techniques are expected to include the Universal Mobile Telecommunications System (UMTS) and UTRA standards. In addition to these longer range techniques, the so-called Bluetooth short-distance wireless technology is also becoming popular in the art, for communication between wireless peripheral devices and computer workstations. Another example of an extended service is General Packet Radio System (GPRS), which is a nonvoice value added service that allows information to be sent and received across a mobile telephone network, for example operating as a GSM or TDMA service, and including such functions as chat, text and image communication, file transfer, home automation, and the like. It is contemplated that these and other wireless standards will be implemented in the industry.
The ability to successful transmit the high data rates required by current and future wireless services depends upon the signal-to-noise ratio at the frequencies of interest. Of course, higher data rates can be attained if the transmission power is increased. However, in order to limit interference among wireless communications, and between wireless transmissions and other radio services, communications standards generally include a specification on the maximum transmission power to be used by a wireless device. These specified power limits can be expressed in many forms, including absolute power levels, a specified power over time profile as in the case of GSM communications, and the like.
In order to maintain operation of a wireless telephone device within the appropriate power specification, as well as for general operating stability and battery life concerns, conventional wireless telephone devices include closed-loop feedback control of power amplifier circuits used for transmission. In general, conventional power amplifier controllers receive a feedback signal corresponding to the current level of power output from the power amplifiers in the device, and compare this measured power output against a desired power level signal to produce an error signal. This error signal is then used to control an input to the power amplifiers so that the output power eventually matches the desired power level.
Conventional power detection circuits for various applications, such as video detector circuits and video receiver circuits, have included semiconductor diode detectors, for example Schottky diode circuits. Examples of such power detectors are described in xe2x80x9cThe Zero Bias Schottky Detector Diodexe2x80x9d, Application Note 969 (Agilent Technologies, Inc., 1999), xe2x80x9cSchottky Barrier Diode Video Detectorsxe2x80x9d, Application Note 923, (Agilent Technologies, Inc., 1999), and xe2x80x9cSurface Mount Zero Bias Schottky Detector Diodes: Technical Dataxe2x80x9d (Agilent Technologies, Inc., 1999). These circuits typically receive radio frequency signal inputs, and the Schottky diode detector effectively produces a voltage that is proportional to the power of the input radio frequency signal. However, conventional Schottky diode detectors are inadequate for use as detectors for power amplifier control in wireless telephones, because the dynamic range of Schottky diode detector circuits is not adequate for this application. For example, in a conventional GSM telephone, the transmission power can vary over a dynamic range of 70 dB. Conventional Schottky diode detectors are incapable of accurately detecting power levels over such a wide dynamic range.
This dynamic range limitation has been addressed by other known power detector circuits for detecting power output in connection with wireless telephones, an example of which is the logarithmic detector. U.S. Pat. No. 6,163,709 discloses an example of a logarithmic detector for detecting power amplifier output in a wireless telephone. As disclosed in this U.S. Pat. No. 6,163,709, the logarithmic detector circuit includes a series of amplifiers that saturate at different current levels. Each amplifier output is connected to a detector circuit that generates an output signal corresponding to the power of the associated amplifier. These output signals are summed to produce the output of the logarithmic detector.
While the logarithmic detector circuit is capable of sensing power levels over a wide dynamic range, the circuit and others like it are quite complex, typically involving several amplifier and detector stages. Accordingly, significant integrated circuit chip area and power are consumed by these conventional power detector circuits. Especially considering the important of conservation of power in battery-powered devices such as wireless telephones, the cost of the logarithmic detector can be substantial.
By way of further background, xe2x80x9cDynamic Range Extension of Schottky Detectorsxe2x80x9d, Application Note 956-5 (Hewlett Packard Co., 1975), reprinted as xe2x80x9cDynamic Range Extension of Schottky Detectorsxe2x80x9d, Application Note 956-5 (Agilent Technologies, Inc., November 1999), discloses that dynamic range of a Schottky diode detector increases with increasing bias current, and that the tangential signal sensitivity (TSS) of such a detector decreases with increasing bias current. This article also discloses that the dynamic range of a Schottky detector can be extended by using a relatively high bias current.
It is therefore an object of the present invention to provide an efficient power detector circuit that operates over a wide dynamic range.
It is a further object of the present invention to provide such a circuit that can be constructed using conventional manufacturing processes.
It is a further object of this invention to provide such a circuit that occupies relatively little integrated circuit chip area.
Other objects and advantages of the present invention will be apparent to those of ordinary skill in the art having reference to the following specification together with its drawings.
The present invention may be implemented into a power amplifier control function for a radio frequency device, such as a wireless telephone. The power amplifier control function includes a Schottky diode power detector circuit, and control circuitry for controlling the bias current applied to the Schottky diode, responsive to the power range within which the power amplifiers are operating. Adjustment of the Schottky diode bias current with increasing and decreasing output power levels provides a wide dynamic operating range for the detector, and thus for the power amplifier control function.